40 degree shoulder (AI)

[_torque_spec_]

I see a lot of rifles cartridges going Ackley Improved. Is that 40 degree should really worth all the hassle? Give me some thoughts/feedback on this. I know you can stuff more powder in the case but why not just choose another cartridge or faster powder or something instead of having to ream your chamber, mod your brass and get custom dies?

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[Goosebrown]

If you're using a given caliber and are successful with it but in testing you find your accuracy node is at the top of the scale, converting to an AI can give you enough velocity to hit a higher node.

That helps mostly in target shooting when you want to reach out farther.

It's not that much hassle. I have a 260ai and I love it

 

[orygun]

No one said going to an Ackley Improved chamber was a practical thing to do. Well, for the most part anyway.
The 280 AI is the standout of the Improved 40 degree designs, but I've found the 30-06 version to be worth the effort.
On the plus side I can achieve near 300 Win Mag velocities with a 22" barrel, 2900 fps with a 180gr bullet. It's also a lighter rifle than it's 300 Win Mag brother and holds one more round in the mag.
The down side is that is IS NOT reliable with standard 30-06 ammo. It's also not quite as simple as reaming the chamber. The barrel has to be removed and set back a turn before it is reamed to the Ackley specs. When it is done the shoulder to neck junction is moved back about .030" from the standard cartridge spec. In theory it creates a "crush zone" that is intended to hold the unimproved cartridge in place for firing. In practice, the support is fairly weak and some (10-15%) of my previously flawless ammo failed to fire.

I am happy with the conversion for the most part and am still sorting out what it really likes. In all honesty, I did it because I thought it would be a fun project I could play with and if I messed it up, it was only going to take a new barrel to fix it.

 

[No_Regerts]

The best part, to me, is not having to trim brass as often.

 

[v0lcom13sn0w]

The best part, to me, is not having to trim brass as often.

yeah i dont like trimming anything often.

 

[No_Regerts]

yeah i dont like trimming anything often.

Like yer muff!

 

[Mooseman]

I tried several AI calibers over the past 40 years and after all the work just to gain a little velocity I found there were standard calibers that performed as well Or Better without the hassles. I can't recall any AI cartridge winning any Competition. I tested the AI , The Herretts, and the Weatherby's for accuracy / velocity , and none met the expectations I demand for accuracy. I got rid of all those guns and went with Standard Loadings in good Rifles and never looked back !

 

[No_Regerts]

I tried several AI calibers over the past 40 years and after all the work just to gain a little velocity I found there were standard calibers that performed as well Or Better without the hassles. I can't recall any AI cartridge winning any Competition. I tested the AI , The Herretts, and the Weatherby's for accuracy / velocity , and none met the expectations I demand for accuracy. I got rid of all those guns and went with Standard Loadings in good Rifles and never looked back !

Kinda sorta. The trend has been less case taper and sharper shoulder angles. Though they are no "improved", new stuff like the 6.5 Creedmoor use many of the same case design principles.

 

[P7M13]

I'm having Velzey convert a 6.5x55 Swede to the 40° shoulder (Ackley never experimented with his conversion on the venerable cartridge).
Looking forward to trying it. Will post comparisons.

 

[Mooseman]

Kinda sorta. The trend has been less case taper and sharper shoulder angles. Though they are no "improved", new stuff like the 6.5 Creedmoor use many of the same case design principles.

Yet... the slim 300 H&H mag won the 1000 yard Competition many years ago , and they extract from the gun easily ! You can't argue with the accuracy of the old 30/06 , the .308 Win, 300 Win mag, and the 50 BMG all having pretty much the same shoulder angle !

 

[No_Regerts]

Yet... the slim 300 H&H mag won the 1000 yard Competition many years ago , and they extract from the gun easily ! You can't argue with the accuracy of the old 30/06 , the .308 Win, 300 Win mag, and the 50 BMG all having pretty much the same shoulder angle !

The youngest cartridge of your bunch is from 1963 and needlessly has a belt. Since then, 6-284, 25-284, 6.5-284, 6x47, 6mm XC, the Creedmoors, all that stuff. Less taper, sharp shoulders, far less recoil because they are more efficient.

6mms probably account for more 1000 yard records over the last 50 years than anything. You have to neck the suck out of the 308 and 30-06.

 

[Mooseman]

7 Experts Discuss Their Precision Caliber of Choice - Ballistic Magazine
An interesting read... 6.5 Creedmoor leads with .260 rem and .223 next , and Beyond 1,000 yards in the extreme and ultra-long-range arena, the .338 Lapua Magnum and .375 CheyTac super magnums are overwhelming favorites. Then they Mention the 300 Win mag.

Here is another article you need to read because it has been tested and proven...
Ammo: Does Case Shape Really Matter? | Gun Digest

 

[osprey]

The advantage of the ai design is slightly more powder capacity and less case stretch with the sharper shoulder angle. These cartridges tend to use their powder charges more efficienly than more traditional designed cartridges. With 280ai, I can reach the same speed as the 7mm mag with 1.5 gr less powder. This is with 160 gr bullets and Rl22 powder in both. I really didnt enjoy fireforming brass my first go around with the 280ai, but I am now a lifer with it since factory brass is available. As always ymmv.

 

[No_Regerts]

7 Experts Discuss Their Precision Caliber of Choice - Ballistic Magazine
An interesting read... 6.5 Creedmoor leads with .260 rem and .223 next , and Beyond 1,000 yards in the extreme and ultra-long-range arena, the .338 Lapua Magnum and .375 CheyTac super magnums are overwhelming favorites. Then they Mention the 300 Win mag.

Here is another article you need to read because it has been tested and proven...
Ammo: Does Case Shape Really Matter? | Gun Digest

Yes, it proves that case capacity rules, and by taking out the taper and reshaping the shoulder, you get more powder and thus more performance/efficiency from the same magazine box.

You mention the 300 H&H. You can't say the 300 Weatherby, essentially a bkown out 300 H&H with a steep radiused shoulder, doesn't outperform the 300 H&H. Thats how the shorter 300 Win Mag can keep pase with the H&H. Plus, if it weren't for the H&H cases and lack of shoulder, we wouldn't have belted cases that have no reason to have a belt and are more prone to case stretch above the belt.

Case design matters.

 

[Certaindeaf]

For turtle shoulders you need to do a lot of shrugs.
That's code for wrong forum.

 

[Mooseman]

Yes, it proves that case capacity rules, and by taking out the taper and reshaping the shoulder, you get more powder and thus more performance/efficiency from the same magazine box.

You mention the 300 H&H. You can't say the 300 Weatherby, essentially a bkown out 300 H&H with a steep radiused shoulder, doesn't outperform the 300 H&H. Thats how the shorter 300 Win Mag can keep pase with the H&H. Plus, if it weren't for the H&H cases and lack of shoulder, we wouldn't have belted cases that have no reason to have a belt and are more prone to case stretch above the belt.

Case design matters.

You apparently did not read the article...
"These tests showed that the Ackley case delivered between 3 and 12 fps more velocity than the .25x60mm C.A., statistically that is a ZERO , especially since the 1.1-grain edge in capacity belonged to the Ackley Improved. All this is in support of Hutton's statement that case shape has no effect on internal ballistics or how the powder is consumed in the process of driving a projectile down the bore."
"So where does the increased velocity come from in an Ackley Improved case design? It's very simple — more case capacity. Ackley did not merely change the shape of the case. He added, in most cases, a fair amount of case capacity, which allows for more powder while holding the overall pressure to the same limits. This added capacity is only available for increased loading after the cases are fireformed to the chamber."
"What pressure does that wildcat operate at?" The answer is, exactly the same pressure as the factory counterpart, or parent case.

Ackley thought he could exceed the pressures of the factory cases … that might be true with antiquated designs like the .30-30 WCF or the .25-35. Cases with a lot of taper were often originally held to lower chamber pressures. It is not true of more modern designs that already have relatively straight walled cases and sharp shoulders, also modern cases normally are designed for higher pressures. A good example of a high pressure design is the .270 Winchester, it was one of the first cases to be loaded to full potential by the factory, modern SAAMI specifications show the .270 at 65,000 psi."
Parker Ackley blew up guns in testing.
The fact remains the AI shoulder blowout only increases powder capacity , it does Nothing for bullet performance and Inexperienced reloaders can place themselves in Harms way with overpressure situations. Brass in any necked cartridge will grow an need trimming, while it may be less growth after each firing it still grows and the brass at the blown out shoulder is also thinner from being stretched.
As far as Belted Magnums, Holland And Holland made them for the simple reason that they reliably extracted after firing a Heavy Magnum load for use in Big Game hunting where like in Africa, a jammed gun or stuck bolt could get you killed.
Case capacity does not "Rule"as faster is not always better ... however proper powder selection, proper bullet selection , and properly prepared matching cases Do rule the competition and accuracy world !
Ackley should have the final word here. "There are no Wildcat cartridges which are actually revolutionary. There are a few which fill gaps between existing commercial cartridges. There are many more which are no better and perhaps not as good as their commercial counterparts.

"There is no evidence which substantiates the claim that one cartridge design is more accurate than another. It certainly cannot be demonstrated that inaccurate barrels can be made more accurate by simply rechambering them to some so-called 'improved' cartridge or Wildcat caliber."

 

[No_Regerts]

You apparently did not read the article...
"These tests showed that the Ackley case delivered between 3 and 12 fps more velocity than the .25x60mm C.A., statistically that is a ZERO , especially since the 1.1-grain edge in capacity belonged to the Ackley Improved. All this is in support of Hutton's statement that case shape has no effect on internal ballistics or how the powder is consumed in the process of driving a projectile down the bore."
"So where does the increased velocity come from in an Ackley Improved case design? It's very simple — more case capacity. Ackley did not merely change the shape of the case. He added, in most cases, a fair amount of case capacity, which allows for more powder while holding the overall pressure to the same limits. This added capacity is only available for increased loading after the cases are fireformed to the chamber."
"What pressure does that wildcat operate at?" The answer is, exactly the same pressure as the factory counterpart, or parent case.

Ackley thought he could exceed the pressures of the factory cases … that might be true with antiquated designs like the .30-30 WCF or the .25-35. Cases with a lot of taper were often originally held to lower chamber pressures. It is not true of more modern designs that already have relatively straight walled cases and sharp shoulders, also modern cases normally are designed for higher pressures. A good example of a high pressure design is the .270 Winchester, it was one of the first cases to be loaded to full potential by the factory, modern SAAMI specifications show the .270 at 65,000 psi."
Parker Ackley blew up guns in testing.
The fact remains the AI shoulder blowout only increases powder capacity , it does Nothing for bullet performance and Inexperienced reloaders can place themselves in Harms way with overpressure situations. Brass in any necked cartridge will grow an need trimming, while it may be less growth after each firing it still grows and the brass at the blown out shoulder is also thinner from being stretched.
As far as Belted Magnums, Holland And Holland made them for the simple reason that they reliably extracted after firing a Heavy Magnum load for use in Big Game hunting where like in Africa, a jammed gun or stuck bolt could get you killed.
Case capacity does not "Rule"as faster is not always better ... however proper powder selection, proper bullet selection , and properly prepared matching cases Do rule the competition and accuracy world !
Ackley should have the final word here. "There are no Wildcat cartridges which are actually revolutionary. There are a few which fill gaps between existing commercial cartridges. There are many more which are no better and perhaps not as good as their commercial counterparts.

"There is no evidence which substantiates the claim that one cartridge design is more accurate than another. It certainly cannot be demonstrated that inaccurate barrels can be made more accurate by simply rechambering them to some so-called 'improved' cartridge or Wildcat caliber."

I think we are talking circles around each other.

 

[Goosebrown]

I can't recall any AI cartridge winning any Competition.

6mm dasher is a 6mm br fire formed to a 40* shoulder and they take most mid range bench rest titles at this point from 600-1000yards

 

[Mooseman]

So, why would anyone spend so much time, effort and money on this wildcat? All you get is a 10% increase in case capacity and a steeper 40 degree shoulder but the downside is, you lose a third of the BR's super-long neck.
Take a look at the stats for the 1000 yard World Benchrest Championships – you'll find every cartridge from the basic 6BR through to the 300WSM and bigger but the Dasher is still the most popular Light Gun cartridge and still holds a World 10-shot Heavy Gun record.
Granted... but it was never an Ackley Cartridge !

 

[_torque_spec_]

Some great posts on here guys. Thanks for all the feedback. It's interesting to here both sides on this.

One question I have is would that steep shoulder effect feeding in semi-auto or select fire rifles? Curious to why the military hasn't adapted this shoulder design